1. Field of Invention
The present invention relates to an illumination system. More particularly, the present invention relates to the lamp holder of a lamp module that has a shorter lamp and a specified curvature radius.
2. Description of Related Art
Due to a rapid increase in processing speed and data storage capacity of computers, processing efficiency of graphic images has improved considerably. Image processing equipment such as optical scanners has an ever-increasing resolution and scanning speed. Flatbed scanner is one of the most common types of scanners in the market. A flatbed scanner has a scanning platform such as a transparent glass panel for putting a scan document or a pattern. To capture the image on the scan document or pattern, an optical scanning module underneath the glass panel moves in parallel to the platform surface. Flatbed scanners are quite popular nowadays because it has a relatively simple structure and easily expandable. Aside from scanning reflective documents or patterns, the flatbed scanner is also suitable for scanning transparent documents such as projection film. Obviously, there are scanners specially made for scanning transparent documents such as positive or negative films having a resolution greater than 2700 dpi. However, these scanners are generally expensive and uncommon.
FIG. 1 is a perspective view of a device for producing a planar light source in a conventional transparent scanner. In general, a planar light source device 100 is equipped with a light-guiding plate 110 and a lamp module 120. The lamp module 120 can be an externally attached module or built into the upper cover of the scanner. The lamp module 120 mainly consists of a lamp 122 and a lamp holder 124. The lamp 122 is, for example, a fluorescent tube for producing a line of light. The lamp 122 is positioned inside the lamp holder 124 and that the lamp 22 has a length identical to the lamp holder 124. The lamp holder 124 is a structure with a curve surface for reflecting light from the lamp 122 to the light-guiding plate 110. The lamp holder 124 has an overall length comparable to the width W of the light-guiding plate 110.
FIG. 2 is a perspective view of a planar light source device in another type of transparent scanner. As shown in FIG. 2, the lamp 122 and the lamp holder 124 are installed above the light-guiding plate 110. The lamp holder 124 has a length and width almost identical to the light-guiding plate 110. Similarly, the lamp holder 124 has a curvature structure. The only difference is that the lamp holder 124 covers a larger area. Due to a larger volume of occupation, the lamp holder 124 is less convenient to use.
In the aforementioned lamp module, light is projected from a lamp onto a surface after reflecting from the lamp holder and passing through the light-guiding plate. This type of lamp module has some disadvantages with regard to weight and cost of production. The lamp must have a length identical to the length of the lamp holder and that the lamp holder must match the length and width of the light-guiding plate. Consequently, not only is the weight of the lamp module increased, but material cost of the lamp module is increased as well.